Precision Electrical Discharge Machining Research Articles

Research on an Intelligent Control Method of a Magnetic Actuator for Micro Electrical Discharge Machining

Electrical discharge machining (EDM) is not limited to the strength and hardness of conductive materials, and is a non-contact special processing technology. In micro-EDM, there are problems such as untimely axial positioning, unstable inter-electrode machining voltage, and difficulty in discharging inter-electrode electric erosion products. This paper considers a magnetic actuator with fast response and high accuracy as the local actuator for a micro-EDM. By introducing a domain adjustment mechanism, a variable domain fuzzy PID controller was designed to control the inter-electrode voltage control system of the magnetic actuator for micro-EDM using an intelligent control strategy. During the micro-EDM machining process, the controlled magnetic actuator drives the tool electrode in the axial direction for rapid micro-positioning, thus maintaining effective inter-electrode machining voltage and achieving a high-speed and high precision EDM. Simulation and experimental results showed that compared with traditional micro-EDM, the machining efficiency of the variable domain fuzzy PID control magnetic actuator, and traditional micro-EDM cooperative control, was increased by 40%, the machining process was more stable, and the quality of the machined surface was better.

Significant Improvements of Machined Surface Qualities by Electrical Multi-channel Discharging in Precision Manufacturing

Electrical discharge machining (EDM) has been widely utilized in manufacturing for decades because of its remarkable advantages of noncontact machining and machining conductive materials of any hardness over traditional manufacturing technologies. However, the original EDM mechanism prevents the further improvements of surface qualities in precision manufacturing. In fact, although current and pulse duration were commonly set to be small to obtain small discharging energy in precision EDM, conventional EDM tools still employ single-channel discharging mechanism to form precise surfaces. This kind of machining concentrates the whole pulse discharging energy on one area, leaving the created crater wide and deep, and surface qualities are difficult to be improved. If the energy of the pulse is separated into several plasma channels, the craters generated by these small energies on the machined surface will be smaller. This kind of machining is called electrical multi-channel discharge machining. It was observed that multi-channel discharging can be formed only when transient arc pulses were generated in the gap. Nevertheless, in precision EDM, it is high probabilities to form stable arc pulses from transient arc pulses damaging machined surface. Therefore, an intelligent strategy should be exploited to realize electrical multi-channel discharging and avoid stable arc pulses occurred as well. To this end, a new adaptive control system of electrical multi-channel discharge machining was studied. Arcing ratio was chosen to be a controlled index and gap-servo voltage was a control variable. Because discharging pulses were transient arc pulses and crates were generated almost in the whole pulse duration, the integrity of the machined surface can be obtained. Experiments demonstrated that surface roughness (SR) on machined 1mm depth can reach up to Ra 0.2μs with a copper electrode of diameter 30mm around 2 hours. The significance of the study is that multi-channel discharging is a new perspective of discharging phenomenon and breaks through the inherent awareness of EDM precision machining in the past years.

An innovation approach of multiple discharging channels in EDM precision machining by a novel adaptive gap voltage control system

For decades, two issues, hard-to-improved machined surface roughness and low machining rate, have hindered the further developments of electrical discharge machining (EDM) Tool in precision manufacturing. In precision EDM, keeping a large gap distance is the only way for conventional EDM to obtain the integrity of a machined surface. However, the fact is large gap distances really prevented further improving machined surface quality and meanwhile lowered machining rate as well. Conversely, this paper tried to take small gap distances so that a discharging mechanism of generating multi-discharging channels from one pulse could be realized. The consequences were that both much greater improved machined surfaces and fast machining rates were obtained in addition to the more integrated machined surface than the conventional EDM did. To this end, a novel EDM adaptive control system was studied in this paper where arcing ratio was a control indicator and gap voltage was a control parameter. By presetting an arcing ratio expected value, arcing ratio can follow the value all the time by adapting gap voltage so that arcing pulses could not take place in the gap and thus the integrity of the machined surface can be obtained. By properly setting arcing ratio expected value, gap voltages could be adapted low enough with respect to arcing ratios so that multi-discharging channels from one pulse could be formed. Comparison experiments not only proved the effectiveness of the EDM adaptive control system but also demonstrated the feasibility of forming multi-discharging channels from one pulse in precision machining. Compared with conventional EDM, in addition to the more integrated machined surface had been obtained the surface roughness had been lowered almost 4 times and the machining rate improved 2.7 times. The significance of the study is that forming multi-discharging channels from one pulse displayed an innovative approach in precision EDM.

Improving surface integrity and surface roughness by forming multi-discharging channels from one pulse in EDM

Conventional electrical discharge machining (EDM) usually took a large gap distance to obtain the integrity of machined surface. However, large gap distances really prevented further improving surface quality and lowered machining efficiency as well. Conversely, this paper took small gap distances in discharging so that discharging from multi-discharging channels could be synchronously realized. To this end, a new adaptive control system for EDM was studied in this paper where arcing ratio was chosen to be a control index and gap servo voltage was a control variable. Arcing ratio was forced to follow a predetermined arcing ratio expectation by adapting gap servo voltage so that arcing pulses could not take place in machining and thus the integrity of the machined surface can be obtained. Compared with conventional EDM, in addition to the more integrated machined surface had been obtained, the surface roughness had been lowered almost 3.5 times and the machining rate improved 2.5 times. Additionally, different forms of multi-discharging channels from one pulse were able to be realized by setting different arcing ratio expectations meeting different requirements of surface roughness. The significance of the study is that forming multi-discharging channels from one pulse displayed an innovative approach in precision EDM.

Thermal analysis for the large precision EDM machine tool considering the spark energy during long-time processing

Thermal error is a major factor influencing the accuracy of large precision electrical discharge machining (EDM) machine tools, especially when processing continuously for a long time. In this paper, a novel thermal analysis model was set up to identify the static and dynamic thermal behaviour of the large EDM machine tool. The thermal effect of multiple spark discharges is considered. An equivalent heat flux method was proposed to model the intermittent heat flux for the first time. Both the steady and transient analyses were applied to investigate the thermal equilibrium time of critical points. It is found that when the study point is far away from the heat source, the longer thermal equilibrium time is needed. And the thermal equilibrium time of the machine tool was also estimated. Verification experiment has been performed, indicating the simulation accuracy of 87 % on the temperature rise of the electrode. Moreover, on the displacement of the spindle, the simulated result matched with the experimental result in Z direction error of 7 %. Finally, suggestions for reducing the thermal deformation were proposed to further improve the machining accuracy of large EDM machine tools.

소형 헬리컬 기어 제조를 위한 분말 압출 금형 제작 및 실험

Extrusion process in the bulk material for fabrication of miniature helical gears has problems such as a high forming load and short tool life because the cross-section is complex and asymmetry. To overcome these problems, in this study, miniature helical gears were fabricated by Zn-22Al powder hot extrusion. The included die angle for minimum extrusion load and improving die filling was determined by FE-simulation. The Zn-22Al spheroidal powder produced by gasatomization were compacted and sintered for extrusion experiment. The dimension of helical-gear is 0.3mm in module, 3.35mm in pitch diameter, <TEX>$15^{\circ}$</TEX> in helix angle and the number of teeth is 12. All of the extrusion experiments were performed with internal helical gear die which was machined by precision electric discharge machining using the electrode. The experiment was conducted at <TEX>$190^{\circ}C$</TEX> to <TEX>$310^{\circ}C$</TEX> to obtain extrusive and mechanical properties. The extruded helical gears were analyzed through extrusion load, Vickers hardness and SEM images for each extrusion temperature. The powder hot extrusion process was successfully applied to fabricate a miniature helical gear.

A study of die helical thread cavity surface finish made by Cu-W electrodes with planetary EDM

An experimental research study intended for the application of a planetary electrical discharge machining (EDM) process with copper-tungsten (Cu-W) electrodes in the surface micro-finishing of die helical thread cavities made with AISI H13 tool steel full-hardened at 53 HRC is presented. To establish the EDM parameters’ effect on various surface finishing aspects and metallurgical transformations, three tool electrode Cu-W compositions are selected, and operating parameters such as the open-circuit voltage (U 0), the discharge voltage (u e), the peak discharge current (i e), the pulse-on duration (t i), the duty factor (τ) and the dielectric flushing pressure (p in), are correlated. The researched machining characteristics are the material removal rate (MRR—V w), the relative tool wear ratio (TWR—ϑ), the workpiece surface roughness (SR—Ra), the average white layer thickness (WLT—e wl) and the heat-affected zone (HAZ—Z ha). An empirical relation between the surface roughness (SR—Ra) and the energy per discharge (W e) has been determined. It is analysed that copper-tungsten electrodes with negative polarity are appropriate for planetary EDM die steel surface micro-finishing, allowing the attaining of good geometry accuracy and sharp details. For die steel precision EDM, the relative wear ratio optimum condition and minor surface roughness takes place at a gap voltage of 280 V, discharge current of 0.5–1.0 A, pulse-on duration of 0.8 μs, duty factor of 50%, dielectric flushing pressure of 40 kPa and copper tungsten (Cu20W80) as the tool electrode material with negative polarity. The copper-tungsten electrode’s low material removal rate and low tool-wear ratio allows the machining of EDM cavity surfaces with an accurate geometry and a “mirror-like” surface micro-finishing. A planetary EDM application to manufacture helical thread cavities in steel dies for polymer injection is presented. Conclusions are appointed for the planetary EDM of helical thread cavities with Cu-W electrodes validating the accomplishment as a novel technique for manufacturing processes.

New EDM polishing and texturing process with conductive polymer electrodes

This paper presents a new hybrid electrical discharge machining (EDM) process, that innovates by the use of a polymer–carbon electrode material which can be molded repeatedly into complex geometries and used to perform precision EDM machining in deionised water. This hybrid EDM process is a novel manufacturing method tailored to perform automated finishing and polishing operations of electrically conductive metal parts with minimum environmental impact. Two distinct hybrid EDM finishing procedures are described in details, namely the “replica” and the “successive imprints” EDM methods. Their main objective is to reduce or completely replace rather tedious and costly hand polishing procedures, which are common practice in the mold making industry. To carry out these new EDM processes, an electrically conductive polymer electrode made of styrene-carbonaceous composite was investigated by design of experiments to minimize its electrical resistivity (0.08 Ω cm) and to maximize its thermal conductivity and formability. A compression molding module was also designed to perform efficiently multiple compression molding cycles of a same electrode. Since water is used as dielectric in the projected EDM processes, a preliminary evaluation of water as a dielectric medium, in conjunction with graphite EDM electrode, was performed. Finally, an experimental simulation of the “replica” method is presented, whereas a P20 tool steel workpiece with a macro-level 0.35 mm Peek-Valley milled surface roughness is smoothed down to a 0.25 mm PV in a single EDM iteration step in deionised water.

A non-silicon micro-machining based scalable fiber optic switch

We report a low-cost non-silicon-based fiber optic switch featuring a novel design of reflection cell, which is capable of ±5 V pulse operation and self-latching. The switch prototypes were measured to have a switch time of 2.6 ms, return loss of −54 dB and a low insertion loss. Enabling technology is precision electrical discharge machining. The dynamic process of switching was analyzed using an FEA software ANSYS for design optimization. A reasonable agreement was obtained between the measurement and calculated results. The switch is scalable to 8×8 or above and allows the realization of high capacity cross-connects.

A non-silicon micro-machining based scalable fiber optic switch

We report a low-cost non-silicon-based fiber optic switch featuring a novel design of reflection cell, which is capable of ±5 V pulse operation and self-latching. The switch prototypes were measured to have a switch time of 2.6 ms, return loss of −54 dB and a low insertion loss. Enabling technology is precision electrical discharge machining. The dynamic process of switching was analyzed using an FEA software ANSYS for design optimization. A reasonable agreement was obtained between the measurement and calculated results. The switch is scalable to 8×8 or above and allows the realization of high capacity cross-connects.